running Catalina and High Sierra on same Mac

[asleyam]

Originally Posted by odamizu

1) If I have High Sierra installed on my Mac and I install Mojave on an external drive, what exactly would be installed on the external drive? Just the System folder? Then the external drive would share the Applications, Library, and Users folders with my Mac? Wouldn't there be a risk of adverse effects and incompatibilities between the two systems?

2) If Apple releases a software update for Mojave, which is on the external drive, how would that work? Would I be alerted the next time I booted from the Mojave drive and the update would be applied to Mojave without affecting the High Sierra system on my Mac?

I am risk-averse and don't want to do anything that might mess up my primary Mac.

Thank you

Before you do anything at all that impacts your mac, do a time machine backup. Then clone your iMac hard drive to an external drive - ssd is best as it will boot and run almost as fast as your internal drive. The clone will be bootable, and it will also allow a complete restore to your internal hard drive should that ever be required.
Now you can install another OSX to another external drive. This will boot into a completely separate osx system. It will see your internal drive as a separate Mackintosh HD. You can safely install apps and operate the external you are booted into without it impacting your internal one. You can see the files in your internal hd as it is treated and mounted like any other attached drive. So drag and drop is fine, but installing etc is confined to your booted drive. If you are a different user in the external boot drive then permissions will likely impact access to your internal files when booted into that external drive. I haven't used that scenario, only as the same user in all drives.

I have an 2019 500gb ssd iMac with Mohave installed. I cloned it to an external samsung ssd. Then I booted the ssd clone and basically treated it as my second iMac. It meant I had to update mohave twice - once when booted into the internal ssd, and again when booted into the clone ssd. I use the clone to test apps like the latest sigil to see how it would look and run compared to the earlier version.

I think if you clone your internal drive, boot into it, then update the osx to that drive it would work for you to test mohave and catalina.

Actually I am so paranoid, I have 2 clones on separate ssds. If one fails I have another one to boot into.

[cedhax]

Originally Posted by odamizu

In that case, my original understanding was incorrect.

Looking at my Mac's directory, I have:

• Applications
• Library
• System
• Users

1) If I have High Sierra installed on my Mac and I install Mojave on an external drive, what exactly would be installed on the external drive? Just the System folder? Then the external drive would share the Applications, Library, and Users folders with my Mac? Wouldn't there be a risk of adverse effects and incompatibilities between the two systems?

2) If Apple releases a software update for Mojave, which is on the external drive, how would that work? Would I be alerted the next time I booted from the Mojave drive and the update would be applied to Mojave without affecting the High Sierra system on my Mac?

I am risk-averse and don't want to do anything that might mess up my primary Mac.

Thank you

Sorry, by user account I was thinking of Apple ID, which you can share on multiple machines anyway. For the local machine's user account, I would pick the same (primary) user name and password to avoid confusion.

Each installed macOS is a self-contained system, with all the four directories you listed above and other hidden directories such as bin, dev, etc. But you can still access Applications on another hard drive.

As long as you install another macOS only on an external hard disk, there is no real risk of messing up your primary OS on the internal hard disk.

[pwalker8]

Originally Posted by odamizu

In that case, my original understanding was incorrect.

Looking at my Mac's directory, I have:

• Applications
• Library
• System
• Users

1) If I have High Sierra installed on my Mac and I install Mojave on an external drive, what exactly would be installed on the external drive? Just the System folder? Then the external drive would share the Applications, Library, and Users folders with my Mac? Wouldn't there be a risk of adverse effects and incompatibilities between the two systems?

2) If Apple releases a software update for Mojave, which is on the external drive, how would that work? Would I be alerted the next time I booted from the Mojave drive and the update would be applied to Mojave without affecting the High Sierra system on my Mac?

I am risk-averse and don't want to do anything that might mess up my primary Mac.

Thank you

When I boot off the external drive, I can't even see the internal drive. I'm sure I can use disk utility to make it accessible, but by default it's not visible. You will need to reinstall all of your programs. You have totally different versions of of all your apps.

I'm sure if it was important, one could tune this all to make it a lot faster, but I find my current set up of keeping an old mac mini for such tasks good enough. For your use, I suspect that eventually, someone will update the De-DRM tools to be 64 bit compatible.

[OtinG]

With High Sierra on one of the two partitions of my Mac Mini 2012 HDD and Windows 10 on the other, both partitions are populated with the system files for the respective OS on it, as well as all app files, personal files, etc. I assume it would partition each Mac OS X the same where it uses only the files on the appropriate partition when you boot into that partition. When booted into the High Sierra partition I can only see that partition and its associated files in Finder. However, I think when booted into the Win 10 partition I can see the files in the High Sierra partition, but I haven't run the Win 10 partition in quite a while so I'm going by memory. When in Win 10 the it is using Windows file system rather than Mac OS X Finder.

One quirk arose after installing Bootcamp and doing the partitions so I could run High Sierra or Win 10. This is likely just a quirk of the Mac Mini though. But the Mac Mini is now a royal PITA when restarted, regardless of whether I restart into the same partition or try to switch partitions. (BTW, switching partitions requires a restart.) This quirk also occurs in other instances. The quirk is that the Mac Mini goes into sleep mode and totally refuses to wake up. This is a well documented issue with some Mac Minis which are not running Bootcamp, but I never encountered it until after installing Bootcamp. So now if I want to restart for an update or any other reasons, chances are it will simply put the screen to sleep and sit there, which eventually requires a hard restart. For updates that can be a true PITA, especially since Apple doesn't keep the blank screen populated with text telling us where we are in the process. It is also a PITA when switching partitions. Most restarts require at least twice as long to complete, especially if restarting for an update. So be forewarned if you have a Mac Mini. Bottom line, if my Mac Mini goes into screen sleep mode for any reason, it cannot be awoken, and I will have to executed a hard restart.

[odamizu]

Thank you pwalker8, cedhax, OtinG and asleyam! I will purchase an external SSD and give this a try

[pwalker8]

I did get dual booting working with USB 3 external hard drive. It's a lot faster than a thumbdrive. I had to reformat the drive with a newer mac than my mac mini, then it worked fine.

As I said, I am unlikely to change using the mac mini for de-drm. It simply takes too long to dual boot, plus I can do stuff on my iMac while the mac mini is doing it's thing. de-drm of movies seems to be limited in speed by iTune rather than the speed of the machine.
de-drm of iBooks is fairly quick. Still, it's a good back up in case something happens to my mac mini. It is a pretty old device.

Eventually, someone will figure out how to do de-drm of iTunes and iBooks with the current Mac OS.

[odamizu]

Originally Posted by asleyam

Before you do anything at all that impacts your mac, do a time machine backup. Then clone your iMac hard drive to an external drive - ssd is best as it will boot and run almost as fast as your internal drive. The clone will be bootable, and it will also allow a complete restore to your internal hard drive should that ever be required ...

Any recommendations on cloning software? SuperDuper? Carbon Copy Cloner? Thx!

[asleyam]

Originally Posted by odamizu

Any recommendations on cloning software? SuperDuper? Carbon Copy Cloner? Thx!

I tried them both and ended up buying Carbon Copy Cloner. It is easy to use and has never failed me over several years and versions of osx. It also has good support and is regularly updated to reflect osx changes.

I have several tasks going that include cloning not only the hard drive (which is automatically made bootable) but also my external ssds which are cloned to folders in a larger external hard drive.

You can try them both and see which one suits you best.

[odamizu]

Thank you, asleyam! If I already have Time Machine backup to an external drive, do I really need a clone backup as well? I understand the Time Machine backup is not bootable? but is that the only issue?

[pwalker8]

Originally Posted by odamizu

Thank you, asleyam! If I already have Time Machine backup to an external drive, do I really need a clone backup as well? I understand the Time Machine backup is not bootable? but is that the only issue?

Depending on space limitations, Time Machine can delete old files. I would certainly back up my home directory to another device first.

My main experience with Time Machine is using the restore from Time Machine when I bought a new machine. It worked fine for that.

[asleyam]

Originally Posted by odamizu

Thank you, asleyam! If I already have Time Machine backup to an external drive, do I really need a clone backup as well? I understand the Time Machine backup is not bootable? but is that the only issue?

If you want to run OSX from an external drive you need a clone of the internal mackintoshHD. One of my older iMacs has a dead internal drive, but the iMac itself is still functional because it boots directly into the external clone and treats it as if it were the internal one.

So basically, if you only need to backup files and restore from time machine, you don't need to clone. But if you want to boot into and work from an external image of your internal drive, then you will need to create a bootable clone.

My backup method is to make daily time machine backups of my internal drive and the 2tb samsung T5 ssd that stores my non system files, to a 3tb hard drive. Using CCC, twice a week I make incremental clones of my internal drive and all my external ssds.
I consider Time machine and CCC to be complementary.

[odamizu]

Originally Posted by asleyam

... One of my older iMacs has a dead internal drive, but the iMac itself is still functional because it boots directly into the external clone and treats it as if it were the internal one.

Oh, wow. I didn't realize one could do something like that. Good to know. Thanks.

So basically, if you only need to backup files and restore from time machine, you don't need to clone.

Got it. I have backup processes already in place. I don't think I need a clone at this time, though knowing what a clone can do is eye-opening and something I will remember for the future.

For now I want to create a bootable external drive running a different macOS (e.g., Catalina beta) than my primary Mac so that I can experiment and test without compromising my primary Mac. Everyone on this thread has been helpful teaching me this. Thank you to all!!

[pwalker8]

Originally Posted by asleyam

If you want to run OSX from an external drive you need a clone of the internal mackintoshHD. ...

You don't need to clone the internal HD to make a bootable external hard drive. Simply choosing the external hard drive via the install works fine. However it makes a clean install with none of the apps or data you may have on your internal hard drive. For the purposes of this discussion, i.e. making an external drive for running a couple of programs, that might be preferable.

You probably don't want to run the external drive time machine to the same disk that you use for the internal drive. That could get a bit confusing. I turned time machine off on my external drive version. No real need to back up anything since it is purely to run a couple of programs and all my data is already saved elsewhere.

[asleyam]

Originally Posted by odamizu

For now I want to create a bootable external drive running a different macOS (e.g., Catalina beta) than my primary Mac so that I can experiment and test without compromising my primary Mac. Everyone on this thread has been helpful teaching me this. Thank you to all!!

I installed Catalina beta in a spare external drive using a usb Catalina installer. Once booted into catalina, disk utility shows 2 containers and when mounted in mohave the external drive (which I named Catalina) appears as 2 volumes. One is Catalina, the other is Catalina - Data.

[kyteflyer]

Originally Posted by odamizu

Got it. I have backup processes already in place. I don't think I need a clone at this time, though knowing what a clone can do is eye-opening and something I will remember for the future.

I didnt think I needed a clone either: I was making one (it was set to auto update weekly) but didn't realise I needed it until the internal drive in my iMac died, and the clone simply took over. I had neither the time, money, nor the energy to cart the iMac in to the shop to have the drive replaced until a month later. It was good to have had that clone working.